1. Field of the Invention
The present invention relates to a numerical controller, and particularly, to a numerical controller that controls a machining tool by analyzing a skiving instruction.
2. Description of the Related Art
A skiving process indicates a machining method of cutting a workpiece by means of a turning tool, wherein the turning tool is fed in a tangential direction of the workpiece to cut the workpiece (JIS standard B0106 0.209). In a skiving process of a turning machine, a workpiece is machined while the Y-axis is moving, using a tool having a straight blade disposed obliquely with respect to the rotation axis of the rotating workpiece (for example, see WO2001/043902).
When such a skiving process is performed by a conventional numerical controller, there is a need to instruct the Y-axis movement in association with the Z-axis movement. FIG. 6 is a diagram illustrating a cutting path of a cutting process performed on the workpiece during the skiving process and a tool movement path during the cutting process performed along the cutting path.
As illustrated in FIG. 6, in the skiving process, the cutting path of the cutting process for the workpiece is set in the rotation axis direction (the Z-axis direction), and the tool performs the cutting process while moving in a direction the straight blade faces (or in a direction substantially orthogonal to the straight blade). For this reason, the tool path is set in the direction of the resultant vector in the Z-axis direction and the Y-axis direction, inclined with respect to the rotation axis direction.
When an operator creates a machining program for the skiving process, two axes, the Z and Y axes, are instructed at the same time by a cutting feed command in order to allow the tool to move along the tool path as illustrated in FIG. 6. However, since a contact point (a cutting point) between the workpiece and the tool is changed depending on the Y-axis position, the instructed tool path does not match the actual machining position. For that reason, the operator needs to create a machining program by calculating the movement amount in the Z and Y axes so as to obtain a desired cutting path, and hence the operator feels a large burden.
Further, since the instructed feed rate is the synthesized velocity in the Z and Y axes and the cutting point is apt to move in the Z-direction depending on the Y-axis position, it is difficult to instruct the cutting point speed to be a desired speed.